1. Field of the Invention
The present invention is directed to a screw tip, and more particularly to a screw tip for controlling the flow of a melt of material in a barrel of a molding system apparatus. For example, the molding system apparatus may be for a plastic injection molding system, or a metal injection molding system for molding a metal in a thixotropic state, or a die casting molding system.
2. Background Information
Screw tip assemblies forming a check valve mounted on the end of a screw are known in the art. For example, U.S. Pat. No. 2,885,734 issued to Wucher on May 12, 1959. The specification illustrates a two part check valve. A diffuser head is formed by a circular disk member that is mounted into an end of a screw. The disk includes a plurality of semi-circular openings around the peripheral edge of the disk. Portions of the disk intermediate the semi-circular openings extend outwardly and engage a inside cylindrical wall of the barrel to provide a seal and support for an end of the screw when located in a barrel. The semi-circular openings cooperate with the inside cylindrical wall of the barrel to form channels that permit a flow of melted material to pass from an upstream side of the diffuser head to a downstream side of the diffuser head. A non-return valve is formed by a second disk member that is mounted on the downstream side of the diffuser head by a threaded bolt. The second disk includes a plurality of circular openings about the face of the disk. The circular openings permit a flow of melted material to pass when spaced apart from the diffuser head, and stop a flow of melted material when engaged with the diffuser head. The circular peripheral edge of the second disk engages the inside cylindrical wall of the barrel to provide a seal and support for the end of the screw in the barrel.
There are a number of problems with the prior art device. The flow path through the check valve includes a number of sharp corners that will shear the melt. The flow path also includes a number of areas that trap melt which in turn leads to degradation of the melt. The screw is supported by the peripheral edge of the check valve and diffuser engaging the inside cylindrical wall of the barrel causing stress and wear of the check valve. The outside surface of the check valve and inside surface of the opening surrounding the threaded bolt in the non-return valve are prone to wear.
Therefore, there is a need for an improved screw tip and check valve